Introduction - Atomic Force Microscopy - page 8

Table 1.1. Comparison of AFM with SEM and TEM.

AFM SEM TEM

Sample preparation little or none from little to a lot from little to a lot

Resolution 0.1 nm 5 nm 0.1 nm

Relative cost low medium high

Sample environment any vacuum(SEM) or gas

(environmental SEM)

vacuum

Depth of field poor good poor

Sample type Conductive or

insulating

conductive conductive

Time for image 2-5 minutes 0.1-1 minute 0.1-1 minute

Maximum field of view 100 m 1 mm 100 nm

Maximum sample size unlimited 30 mm 2 mm

Measurements 3 dimensional 2 dimensional 2 dimensional

measured. With an AFM, if the probe is good, a good image is measured. Because TEM
and SEM usually operate in a vacuum, and require a conductive sample (so non-conductive
samples are usually coated with a metallic layer before imaging), AFM has the advantage
of being able to image the sample with no prior treatment, in an ambient atmosphere. This
makes scanning quicker, and can also mean fewer artefacts are introduced by the vacuum
drying, or the coating procedure. On the other hand, AFM image recording is usually
slower than an SEM, so if a large number of features on one sample are required, AFM
may be considerably slower than SEM for the same sample.
As we will see in the following chapters, AFM can be used for much more than
measuring images, however. One of the unique advantages of SPM techniques is the
highly accurate positioning of the probe on or close to the sample surface. This has become
an enabling technology for the measurement and manipulation of samples on the nanos-
cale. AFM's other key advantages are its very high sensitivity, and the fact that the smaller
the instrument, the more sensitive it can be. This is the opposite of all previous tools, and
means that AFM integration with other techniques is very simple.